Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
1999-03-31
2001-10-30
Snow, Walter E. (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S165000, C324S207210
Reexamination Certificate
active
06310474
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method of sensing direction of crankshaft rotation and more particularly to a method and apparatus to sense direction of crankshaft rotation from the passage of single tooth edges of an encoder or target wheel with a single, currently used, differential sequential sensor employing either Hall elements or magnetoresistors.
BACKGROUND OF THE INVENTION
It is well known in the art that the resistance modulation of Hall elements or magnetoresistors can be employed in position and speed sensors with respect to moving ferromagnetic materials or objects (see for example U.S. Pat. Nos. 4,835,467; 4,926,122; and 4,939,456).
Increasingly more sophisticated spark timing and emission controls introduced the need for crankshaft sensors capable of providing not only precise position information, but also, during cranking, a direction of rotation signal. Currently, as shown in
FIG. 1
, direction of rotation, clockwise (CW)
32
or counterclockwise (CCW)
34
, is most commonly obtained from an encoder wheel
10
, also called a target wheel, having a plurality of teeth
12
and slots
14
of essentially equal length which have a spacing between adjacent teeth or a spacing between adjacent slots of P, called the tooth/slot pitch. The teeth
12
and slots
14
are sensed by SENSOR
1
16
and SENSOR
2
18
in quadrature (i.e. with spacing between sensors equal to one-quarter of the tooth/slot pitch P). Equal lengths of teeth
12
and equal lengths of slots
14
and the one-quarter pitch spacing between sensors are preferred, but not absolutely necessary. The square wave output signals from SENSOR
1
16
and SENSOR
2
18
are fed as a clock input
20
and a data input
22
into a D type FLIP-FLOP
24
whose output
26
provides a direction indication and is either high (H)
28
or low (L)
30
depending on the direction of rotation of the target wheel
10
. Due to the large P/4 distance between SENSOR
1
16
and SENSOR
2
18
, a major disadvantage of the current method is the inability to detect the change of rotational direction of the target wheel when a single tooth edge, such as tooth edge
36
, is oscillating around a single sensor, such as SENSOR
1
16
. In this case, SENSOR
1
16
would detect the back and forth oscillating single tooth edge
36
as the rising and falling edges of passing teeth
12
. Since the direction indication
26
would remain unchanged, serious position errors would be generated. For this reason, and due to the necessity of adding a second sensor, the conventional method of detecting direction of rotation is not suitable for automotive crankshaft sensors.
What is needed is a method and apparatus whereby the direction of rotation of an automotive crankshaft can be obtained from the passage of a single tooth edge of a target wheel.
SUMMARY OF THE INVENTION
The present invention provides detection of direction of rotation via the outputs of a differential sequential sensor employing two matched sensing elements, either Hall elements or magnetoresistors (MRs), to extract direction of rotation information from the passage of a single tooth edge of a target wheel. The two matched sensing elements are spaced in close proximity to each other, preferably on the order of about 1 mm to 2 mm apart, in the circumferential direction of the target wheel and generate two identical angularly offset signals from the passage of a single tooth edge of a target wheel which are input to a signal conditioning circuit. Within the signal conditioning circuit, the two sensor signals are differentially amplified to produce a differential signal whereby the polarity of the differential signal enables one of two comparators with respective reference voltages. The output of the enabled comparator is processed and converted into a digital output signal whose voltage level indicates the direction of rotation of the target wheel.
Accordingly, it is an object of the present invention to provide a digital output voltage for detecting direction of rotation of a target wheel at a single tooth edge.
It is an additional object of the present invention to provide a digital output voltage for detecting direction of rotation of a target wheel at a single tooth-slot edge using two closely spaced sensing elements.
These, and additional objects, advantages, features, and benefits of the present invention will become apparent from the following specification.
REFERENCES:
patent: 4992733 (1991-02-01), Griebeler
Delphi Technologies Inc.
Dobrowitsky Margaret A.
Snow Walter E.
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